14Not until halfway through the Feast did Jesus go up to the temple courts and begin to teach. 15The Jews were amazed and asked, "How did this man get such learning without having studied?"
16 Jesus answered, "My teaching is not my own. It comes from him who sent me. 17 If anyone chooses to do God's will, he will find out whether my teaching comes from God or whether I speak on my own. 18 He who speaks on his own does so to gain honor for himself, but he who works for the honor of the one who sent him is a man of truth; there is nothing false about him. 19 Has not Moses given you the law? Yet not one of you keeps the law. Why are you trying to kill me?"
Another instance of Jesus bringing up the law. Even speaking to religious Jews, He says that not one of them has kept the law. The only way they are going to really know that Jesus is who He says He is, is to do the will of God. When you make that decision, God will give you a new heart with new desires that are pleasing to Him. Jesus doesn't argue apologeticics with them, but appeals to their conscience through the law.
20 "You are demon-possessed," the crowd answered. "Who is trying to kill you?"
21 Jesus said to them, "I did one miracle, and you are all astonished. 22 Yet, because Moses gave you circumcision (though actually it did not come from Moses, but from the patriarchs), you circumcise a child on the Sabbath. 23 Now if a child can be circumcised on the Sabbath so that the law of Moses may not be broken, why are you angry with me for healing the whole man on the Sabbath? 24 Stop judging by mere appearances, and make a right judgment."
Many times when presenting the Gospel to people I am told that I should not judge. To be clear, I am only pointing out God's judgment and not judging people myself. But, Jesus is very clear many times when He talks about judgment that we ARE to judge, and especially to judge by a right standard. That standard is God's law. It is a mirror by which we are to judge ourselves. No matter how religious we are, we come up far short of perfection. God makes it clear that we are going to be judged by that standard.